Move kombu as a test dependency only

oslo.messaging has kombu in its own requirements, so kombu
is not needed in requirements.txt.
Instead it was moved to test-requirements.txt file because
it is explicitly imported for functionnal tests.

Change-Id: I952263f1d2c61a3b700824914da499b1ece91b78

requirements.txt

@@ -9,7 +9,6 @@ cryptography>=1.0 # Apache-2.0
 eventlet>=0.17.4
 greenlet>=0.3.2
 keystonemiddleware!=2.4.0,>=2.0.0
-kombu>=3.0.7
 lxml>=2.3
 netaddr!=0.7.16,>=0.7.12
 oslo.cache>=0.8.0 # Apache-2.0

test-requirements.txt

@@ -6,6 +6,7 @@
 hacking<0.11,>=0.10.0
 bandit>=0.13.2
 coverage>=3.6
+kombu>=3.0.7
 mock>=1.2
 mox3>=0.7.0
 PyMySQL>=0.6.2 # MIT License