check-filesystem assumed that UHD's version string always had the format
of <version>-<git_count>-<git_hash>. However, this is not always the
case; see ./host/cmake/Modules/UHDVersion.cmake for more details.
Instead of trying to parse the version string into components, just
check to make sure the version and git hash are present in the version
string.
If the mender utility is not installed or exits with a failure, return
NULL for the artifact rather than raising an exception (and disrupting
device initialization).
