Fix regression for the case of COSMOVISOR_ENABLED without START_CMD

[orenl-lava]

This fixes a glitch in commit 3aacc34.

When starting without args and without START_CMD, the command for regular (as-is) and snapshot are "$PREFIX_CMD $PROJECT_BIN start", whereas for cosmovisor it should be "$PREFIX_CMD start".

Fix using a new DEFAULT_CMD that is set together with PREFIX_CMD based on the selected mode.

[PikachuEXE]

I am running one node with both COSMOVISOR_ENABLED and SNAPSHOT_PATH present
Does this new script only run cosmovisor?

[tombeynon]

I've taken a stab at this in #576 - it retains the previous support for COSMOVISOR_ENABLED AND SNAPSHOT_PATH, and gives the user full control by overriding the docker command if required.

This seems the most sensible route to me, but could you both have a look and make sure it covers all your use cases @orenl-lava @PikachuEXE ?

[orenl-lava]

I am running one node with both COSMOVISOR_ENABLED and SNAPSHOT_PATH present
Does this new script only run cosmovisor?

Sorry, I did not consider this possibility.

IIUC, previously if you set both, then the it would execute snapshot.sh cosmovisor run start.
Before fixing this, let's agree on the desired semantics:

Snap = snapshot
Cosm = cosmovisor

BIN = $PROJECT_BIN

           |                                command to execute
  given    |   ----------   ----------------------   -------------------------   -------------------------------------
  args     |     normal             snap                     cosm                           snap+cosm
---------- |   ----------   ----------------------   -------------------------   -------------------------------------
args($@)   |   "$@"         snapshot.sh "$@"         cosmovisor run "$@"         snapshot.sh cosmovisor run "$@"
$START_CMD |   $START_CMD   snapshot.sh $START_CMD   cosmovisor run $START_CMD   snapshot.sh cosmovisor run $START_CMD
no args    |   $BIN start   snapshot.sh $BIN start   cosmovisor run start        snapshot.sh cosmovisor run start

So this supports 4 preset modes of operation (normal, snapshot, cosmovisor, and snapshot+cosmovisor), and 3 types of arguments (no args, command line args, and env-var START_CMD). Anything beyond can be controlled via args or START_CMD.

@PikachuEXE does this cover your use cases? If so, I'll push a fix so we can close this.

[PikachuEXE]

I have tested #576 & responded there so you can check that one first before making changes

[tombeynon]

I'm going to go ahead with #576 now, partly because we've broken a few things with the previous release so need to get a fix out quickly, and partly because I think it's important the docker command can override any other behaviour. Closing this PR but please re-open against master if anything else needs changing