The MOCK_HOSTNAME is not sufficiently long to guarantee that it is
longer than the hostname on the current host.  Make it crazy long.
BUG: The MOCK_HOSTNAME is not sufficiently long.

Extend the MOCK_HOSTNAME for a better chance that it will be longer
than the actual hostname.
Merge pull request #12578 from plastikos/bug-longer_mock_hostname

BUG: longer MOCK_HOSTNAME is not sufficiently long