0.1.43

Klibs: AWS CloudWatch: add support for sending logs

This change implements a new console driver that sends log messages
to AWS CloudWatch when Nanos runs on an AWS instance.
This feature is enabled by loading the cloudwatch and tls klibs and
adding a "logging" tuple to the "cloudwatch" tuple in the root
tuple. The "logging" tuple may contain the following attributes:
- "log_group": specifies the CloudWatch log group to which log
messages should be sent; if not present, the log group is derived
from the image name (taken from the environment variables), or from
the name of the user program if no IMAGE_NAME environment variable
is present
- "log_stream": specifies the CloudWatch log stream to which log
messages should be sent; if not present, the log stream is derived
from an instance identifier (e.g.
'ip-172-31-23-224.us-west-1.compute.internal')
The log group and the log stream are automatically created if not
existing.

In order for the cloudwatch klib to retrieve the appropriate
credentials needed to communicate with the CloudWatch Logs server,
the AWS instance on which it runs must be associated to an IAM role
with the CloudWatchAgentServerPolicy, which must grant permissions
for the logs:PutLogEvents, logs:CreateLogGroup, and
logs:CreateLogStream actions, as described in
https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/iam-access-control-overview-cwl.html

Example contents of Ops configuration file:
```
"ManifestPassthrough": {
  "cloudwatch": {
    "logging": {"log_group":"my_log_group","log_stream":"my_log_stream"}
  }
}
```