[GH-86] Add requirement license info.

Add license information for each dependencies listed in requirements.txt.
And add a `requirements.os.txt` file for dependency downloading under
openstack cinder/manila environments.

requirements.os.txt

@@ -0,0 +1,9 @@
+## Recommend to download these files with "--no-deps" option, e.g.
+##   pip download --no-deps -r <path to>/requirements.os.txt
+future>=0.15.1 # MIT
+python-dateutil>=2.4.2 # BSD
+retryz>=0.1.8 # Apache-2.0
+cachez>=0.1.0 # Apache-2.0
+bitmath>=1.3.0 # MIT
+queuelib>=1.4.2 # BSD
+storops # Apache-2.0

requirements.txt

@@ -1,10 +1,11 @@
-future>=0.15.1
-paramiko>=1.13.0
-python-dateutil>=2.4.2
-PyYAML>=3.11
-requests!=2.9.0,>=2.8.1
-retryz>=0.1.8
-cachez>=0.1.0
-six>=1.9.0
-bitmath>=1.3.0
-queuelib>=1.4.2
+paramiko>=1.13.0 # LGPLv2.1+, cinder, manila
+requests!=2.9.0,>=2.8.1 # Apache-2.0, cinder, manila
+PyYAML>=3.11 # MIT, cinder, manila
+six>=1.9.0 # MIT, cinder, manila
+
+future>=0.15.1 # MIT
+python-dateutil>=2.4.2 # BSD
+retryz>=0.1.8 # Apache-2.0
+cachez>=0.1.0 # Apache-2.0
+bitmath>=1.3.0 # MIT
+queuelib>=1.4.2 # BSD