Remove lxml as a forced depend

keystoneclient only needs lxml for saml support, which is an
optional contrib piece. Since keystoneclient is massiely used, and
as lxml is a big beefy depend that requires C compilers, move
lxml to test-requriements.

Change-Id: I01b6b702fb8f414884cb1da306d5b95406e86513

requirements.txt

@@ -1,7 +1,6 @@
 argparse
 Babel>=1.3
 iso8601>=0.1.9
-lxml>=2.3
 netaddr>=0.7.6
 oslo.config>=1.4.0.0a3
 oslo.utils>=0.1.1

test-requirements.txt

@@ -3,6 +3,7 @@ discover
 fixtures>=0.3.14
 hacking>=0.8.0,<0.9
 keyring>=2.1,!=3.3
+lxml>=2.3
 mock>=1.0
 mox3>=0.7.0
 oauthlib>=0.6