webadmin: making RegexValidation testable

This patch change the call to Regex#IsMatch(String,String,RegexOptions)
within RegexValidation with a call to Regex#IsMatch(String,String).

The problem is that Regex#IsMatch(String,String,RegexOptions) isn't
implmenented (throws NotImplementedException) in Regex class that is
located in compat project, thus classes that inherits RegexValidation
can't be tested with unit tests.

From the UI perspective this patch doesn't change much because in the
Regex class of the UI (located in gwt-extension) the method
Regex#IsMatch(String,String) calls
Regex#IsMatch(String,String,RegexOptions) with RegexOptions.None.

Change-Id: Ib35b0b1a4b7a29902a65986e1ceadf231a9a8c50
Signed-off-by: Arik Hadas <ahadas@redhat.com>