contint: switch localvhost to apache::conf

/etc/apache2/conf.d/ no more exists on Trusty.  Luckily apache::conf is
a thin wrapper that let us move the definition under conf-available and
conf-enabled.

Should fix an error on integration-slave1006-trusty.eqiad.wmflabs
because /etc/apache2/conf.d/ does not exist.

Bug: 68256
Change-Id: I76eaf3661dc7e34d9737892172f76a1e592c34e0
Merge "contint: switch localvhost to apache::conf" into production