Fixes issue preventing VmAccess from uninstalling

[jscalev]

VmAccess uninstall fails because the agent always sends a sequence number of 0 to uninstall, but there is not corresponding .settings file. Therefore, we throw an exception when trying to load the settings and fail.

The fix here is to replace the script used for commands other than enable with one that does nothing, since there is no business logic for these commands.

We also need to set continueOnUpdateFailure to true, so during the upgrade WALA ignores the fact that the uninstall for the previous (problematic) version fails.

[mayankdaruka-msft]

I feel like it's a good idea to get rid of the sequence number dependency for all operations except Enable, what do you think?

We are making this logic more complex, when in fact we don't really need to even parse handler context for install/update/disable/uninstall. Reporting status is not necessary, especially given the 4 operations don't contain any business logic and should be succeeding in all cases.

As per this table, WALA does not expect an extension to report status in any case except enable.

[narrieta]

@mayankdaruka-msft - careful with that table; it is not accurate. I noticed that yesterday. WALinuxAgent will pickup any status file reported by the extension on any operation.

But as far as this specific issue, the point you are making about getting rid of the dependency on the extension settings for operations that don't need them is very valid.

Now, if those operations do not have business logic and should always succeed, another alternative is to point them to a dummy script that just "exit 0"

[jscalev]

I've removed all commands other than enable and followed the suggestion of adding a dummy script with 'exit 0'