admin checks for email addresses should be case-insesitive

[tyll]

For user remi the check in FAS did not work because FAS stores the address in different case than bugzilla. Maybe FAS should store the address in lowercase but afaik the local part might be case-sensitive in theory but I do not believe anyone does this actually.

[pypingou]

So ftr, FAS has Fedora@Famille... while bugzilla has fedora@famille... so indeed searching FAS w/ the bz email doesn't work.