implementation specific requirement files

current requirements.txt file lists all the dependency files
which will install libraries which are not needed if one choose
to use a different implementation. For example, one can use
v2 reference implementation or elastic search implementation.
not having separate files, one will install many libraries.
For elastic search implementation, one will not wish to install
influxdb dependencies. But without separate requirement files,
it won't be possible to do that. With this change, one can
simply use implementation specific requirement file to
accomplish that. To install v2 reference implementation, simply
run this command:
   pip install -r requirements.txt -r ref-impl-requirements.txt

To install elastic search implementation, simply run this command:
   pip install -r requirements.txt -r es-impl-requirements.txt

Change-Id: I59cd53f934237a76545975361c2d41415e17fa05

es-impl-requirements.txt

@@ -0,0 +1,8 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, please pay attention to order them correctly.
+#
+# This is the dependency file for elasticsearch implementation which based on
+# elasticsearch, all elasticsearch related dependencies should be listed here.
+
+requests>=1.1

ref-impl-requirements.txt

@@ -0,0 +1,11 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, please pay attention to order them correctly.
+#
+# This is the dependency files for v2 reference implementation which based on
+# influxdb and mysql. All dependencies related to v2 reference implementation
+# should be listed here.
+
+influxdb>=0.1.12
+MySQL-python
+Pyparsing>=2.0.3

requirements.txt

@@ -1,12 +1,31 @@
+# The order of packages is significant, because pip processes them in the order
+# of appearance. Changing the order has an impact on the overall integration
+# process, please pay attention to order them correctly.
+
+# this is the base monasca-api requirements. To choose a particular
+# implementation to install, run pip install -r xxx-requirements.txt.
+#
+# for example, to install monasca-api and v2 reference implementation, do the
+# followings:
+#
+#    pip install -r requirements.txt -r ref-impl-requirements.txt
+#
+# The above will install monasca-api base and reference implementation
+# dependencies.
+#
+# To install monasca-api and elasticsearch implementation, do the following:
+#
+#    pip install -r requirements.txt -r es-impl-requirements.txt
+#
+# The above command will install monasca-api base and elasticsearch
+# implementation while leave other implementation dependencies alone.
+
 falcon>=0.1.9
 gunicorn>=19.1.0
-influxdb>=0.1.12
-MySQL-python
 oslo.config>=1.2.1
 pastedeploy>=1.3.3
 pbr>=0.6,!=0.7,<1.0
-Pyparsing>=2.0.3
-simplejson>=2.0.9
+python-dateutil>=1.5
 six>=1.7.0
 stevedore>=0.14
 ujson>=1.33