Use TYPE_GAUGE rather than TYPE_CUMULATIVE

For hardware network bandwidth metering, it uses TYPE_CUMULATIVE, but
the oid "1.3.6.1.2.1.2.2.1.5"(in file ceilometer/hardware/inspector/snmp.py)
it walks in net-snmp.org is representing ifSpeed and the type is GAUGE.

Cumulative definition: Increasing over time, but when i run
`ceilometer sample-list --meter hardware.network.bandwidth.bytes`
the output is not increasing over time.

reference:
http://docs.openstack.org/developer/ceilometer/measurements.html
http://www.net-snmp.org/docs/mibs/interfaces.html

Change-Id: Ic8a8280695c25db103fe4e4592fe00622728655d
Closes-Bug: #1326723
Adds caches for image and flavor in compute agent

Currently to obtain image and flavor data,
compute agent always calls nova api, even for the same id of image/flavor.
In order to reduce the number of nova-client call, caches for image and flavor
are introduced.

The caches only live in a local scope of _with_flavor_and_image: created every
single polling interval and thrown away at the end of the interval.
Although the caches only live in a short time, they are effective because same
flavors are used many times in one compute-node in typical use cases.

Change-Id: I63b6a59f06be4911f39073e34cfc3a2a7b832c51
Closes-bug: #1293337
Adding alarm list filtering by state and meter

Adding alarm list filtering by state for SQLAlchemy, PyMongo and
HBase drivers
Adding alarm list filtering by meter only for SQLAlchemy and PyMongo
drivers.

Closes-Bug: #1224298

Change-Id: I393e2988142878d33363438671c240199ede65a4
remove default=None for config options

In the cfg module default=None is set as the default value.

Change-Id: I65786401354e5fb966339cbdb4a76f5f628b8d6f
Closes-Bug: #1323975
Merge "Adds caches for image and flavor in compute agent"
Merge "Use TYPE_GAUGE rather than TYPE_CUMULATIVE"
Merge "remove default=None for config options"
Merge "Adding alarm list filtering by state and meter"