In case CommandCapabilities is called from a command
that does not exist and raise_on_error is requested
make sure to provide a better error message pointing
out that the command does not exist instead of the
misleading "Could not parse ... output" error message
The class allows to check for data produced on stdout
and stderr. However, programs reporting data on stderr
usually fails with an exit code != 0. If the command
is not called with raise_on_error=False it will never
be possible to catch information from stderr. As we
don't know if programs returns a failed exit code
even on their e.g --usage message we should always
pass the no raise option to make this more useful
This commit ensures that when trying to parse the version of a tool
the comparison is done with the longest match for the given regular
expression. This solves cases such in `grub2` where the tool name
already provides some digit that could be seen as a version.
