Honor user specified extra gpg keyrings

Closes: #224

Until now, we were only using the system path for apt keyring. But there
have been multiple reports of the possibility of keyrings being
scattered across the file system.

As such, introduce an `--extra-keyring` option and let the user specify
a directory path where extra keyrings are stored

apt_offline_core/AptOfflineCoreLib.py

@@ -702,33 +702,38 @@ def __init__(self, gpgv=None, keyring=None, Simulate=False):
             self.gpgv = gpgv
 
         self.opts = []
-        if keyring is None:
-            self.opts.append("--ignore-time-conflict")
-            for eachPath in self.defaultPaths:
-                if os.path.isfile(eachPath):
-                    if eachPath.endswith(".asc"):
-                        self.DearmorSig(eachPath)
-                    elif eachPath.endswith(".gpg"):
-                        self.opts.extend(["--keyring", eachPath])
-                elif os.path.isdir(eachPath):
-                    for eachGPG in os.listdir(eachPath):
-                        if eachGPG.endswith(".asc"):
-                            eachGPG = os.path.join(eachPath, eachGPG)
-                            self.DearmorSig(eachGPG)
-                        elif eachGPG.endswith(".gpg"):
-                            eachGPG = os.path.join(eachPath, eachGPG)
-                            log.verbose(
-                                "Adding %s to the apt-offline keyring\n" % (
-                                    eachGPG)
-                            )
-                            self.opts.extend(["--keyring", eachGPG])
-            if len(self.opts) == 1:
-                log.err(
-                    "No valid keyring paths found in: %s\n"
-                    % (", ".join(self.defaultPaths))
-                )
-        else:
-            self.opts.extend(["--keyring", keyring, "--ignore-time-conflict"])
+        self.opts.append("--ignore-time-conflict")
+
+        for eachPath in self.defaultPaths:
+            if os.path.isfile(eachPath):
+                if eachPath.endswith(".asc"):
+                    self.DearmorSig(eachPath)
+                elif eachPath.endswith(".gpg"):
+                    self.opts.extend(["--keyring", eachPath])
+            elif os.path.isdir(eachPath):
+                for eachGPG in os.listdir(eachPath):
+                    if eachGPG.endswith(".asc"):
+                        eachGPG = os.path.join(eachPath, eachGPG)
+                        self.DearmorSig(eachGPG)
+                    elif eachGPG.endswith(".gpg"):
+                        eachGPG = os.path.join(eachPath, eachGPG)
+                        log.verbose(
+                            "Adding %s to the apt-offline keyring\n" % (
+                                eachGPG)
+                        )
+                        self.opts.extend(["--keyring", eachGPG])
+
+        if len(self.opts) == 1:
+            log.err(
+                "No valid keyring paths found in: %s\n"
+                % (", ".join(self.defaultPaths))
+            )
+
+        if keyring:
+            for eachFile in os.listdir(keyring):
+                extraKeyringFile = os.path.join(keyring, eachFile)
+                log.verbose("extraKeyringFile is %s" % extraKeyringFile)
+                self.opts.extend(["--keyring", extraKeyringFile, "--ignore-time-conflict"])
 
     def DearmorSig(self, asciiSig):
         gpgCmd = []
@@ -1800,6 +1805,7 @@ def __init__(self, args):
             self.Bool_SkipChangelog = args.skip_changelog
             self.tempdir = tempfile.gettempdir()
             self.Bool_StrictDebCheck = args.strict_deb_check
+            self.extra_keyring = args.extra_keyring
 
             if not os.access(self.tempdir, os.W_OK):
                 log.err(
@@ -2210,7 +2216,7 @@ def displayBugs(self, dataType=None):
                     sys.exit(1)
 
         def verifyAptFileIntegrity(self, FileList):
-            self.AptSecure = APTVerifySigs(
+            self.AptSecure = APTVerifySigs(keyring=InstallerInstance.extra_keyring,
                 Simulate=InstallerInstance.Bool_TestWindows)
 
             self.lFileList = FileList
@@ -3103,6 +3109,14 @@ def main():
         default=None,
     )
 
+    parser_install.add_argument(
+        "--extra-keyring",
+        dest="extra_keyring",
+        help="Extra Keyring path to include for.",
+        metavar="/etc/apt/keyring/",
+        default=None,
+    )
+
     parser_install.add_argument(
         "--skip-bug-reports",
         dest="skip_bug_reports",