Sort requirements.txt to be more readable

Sort file requirements.txt as we did in file test-requirements.txt.

Change-Id: Ie28f21c37c47090c97ee4c047ce440af4f57dbea

requirements.txt

@@ -1,24 +1,24 @@
-pbr>=0.5.21,<1.0
-PasteDeploy>=1.5.0
-WebOb>=1.2.3,<1.3
+anyjson>=0.3.3
+argparse
+Babel>=1.3
 eventlet>=0.13.0
 greenlet>=0.3.2
-requests>=1.1
-Routes>=1.12.3
-PrettyTable>=0.7,<0.8
 iso8601>=0.1.8
-anyjson>=0.3.3
+Jinja2
 kombu>=2.4.8
 lockfile>=0.8
-argparse
-stevedore>=0.12
-sqlalchemy-migrate>=0.8.2
-SQLAlchemy>=0.7.8,<=0.7.99
-qpid-python
-six>=1.4.1
 netaddr>=0.7.6
-pycrypto>=2.6
-Babel>=1.3
-pycadf>=0.1.9
-Jinja2
 oslo.config>=1.2.0
+PasteDeploy>=1.5.0
+pbr>=0.5.21,<1.0
+PrettyTable>=0.7,<0.8
+pycadf>=0.1.9
+pycrypto>=2.6
+qpid-python
+requests>=1.1
+Routes>=1.12.3
+six>=1.4.1
+SQLAlchemy>=0.7.8,<=0.7.99
+sqlalchemy-migrate>=0.8.2
+stevedore>=0.12
+WebOb>=1.2.3,<1.3