Allow '@' in tag values
Allow '@' in tag values

This allows using an email address (as is) as part of a tag. The main
problem that could arise is when parsing tags from a shell script, but
(AFAIK) '@' is not a special character when used in values (happy to be
corrected if not true).

The patch also moves the re to be compiled at class init time, should
use less resources; in my tests it is fine to use a compiled re from
multiple threads.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>

dimara/ganeti,grnet/snf-ganeti,leshchevds/ganeti,ganeti/ganeti,ganeti/ganeti,ganeti/ganeti,andir/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/snf-ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,bitemyapp/ganeti,mbakke/ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti,mbakke/ganeti,apyrgio/ganeti,yiannist/ganeti,yiannist/ganeti,mbakke/ganeti,grnet/snf-ganeti,yiannist/ganeti,onponomarev/ganeti,dimara/ganeti,leshchevds/ganeti,andir/ganeti,apyrgio/ganeti,leshchevds/ganeti,andir/ganeti