Harden PPA defined type

Harden PPA defined type

Prior to this commit there was a possibility that malformed strings
could be passed as the resources name. This could lead to unsafe
executions on a remote system.

This was also a possibility for the options parameter as it was
constrained to a string.

In addition, commands were not properly broken out in to arrays of
arguments when passed to the exec resource.

This commit fixes the above by adding validation to the resource name
ensuring that the given ppa name conforms to expectation. Also, commands
are now broken down in to arrays of arguments appropriately. This ensures
safer execution on the remote system.

Given that the options parameter, passed as a raw string, could lead to
unsafe code execution it was reasonable to change the accepted type to
an `Optional[Array[String]]. This means that an array of options can now
be passed to the exec resource inside the original command.