storage:util:upgrade: Strip any trailing space from the version

storage:util:upgrade: Strip any trailing space from the version

Not just '\n'.  Mark Mikofski reported an error on the upgrade from
1.4 to 1.5 on MS Windows:
> upgrading bugdir from "Bugs Everywhere Directory v1.4" to "Bugs Everywhere Directory v1.5"
> Traceback (most recent call last):
>   ...
>   File "c:\...\libbe\storage\util\upgrade.py", line 141, in check_initial_version
>     assert version == self.initial_version, '%s: %s' % (path, version)
> AssertionError: c:\...\.be\version: Bugs Everywhere Directory v1.4
>
> **notes:** I set a breakpoint and it does seem that they are not the same
> (Pdb) self.initial_version
> 'Bugs Everywhere Directory v1.4'
> (Pdb) version
> u'Bugs Everywhere Directory v1.4\r'

We don't need to convert to Unicode, because on Python 2.7:

  $ python2.7 -c "print('a' == u'a')"
  True

Strange, but true ;).  One day we'll migrate BE to Python 3...