Merge lp://qastaging/~mthaddon/charms/trusty/nova-compute/disk-cachemodes into lp://qastaging/~openstack-charmers-archive/charms/trusty/nova-compute/next

UOSCI bot says:
charm_lint_check #1106 nova-compute-next for mthaddon mp241941
    LINT OK: passed

LINT Results (max last 5 lines):
  I: config.yaml: option os-data-network has no default value
  I: config.yaml: option config-flags has no default value
  I: config.yaml: option instances-path has no default value
  W: config.yaml: option disable-neutron-security-groups has no default value
  I: config.yaml: option migration-auth-type has no default value

Full lint test output: http://paste.ubuntu.com/9055857/
Build: http://10.98.191.181:8080/job/charm_lint_check/1106/

UOSCI bot says:
charm_unit_test #940 nova-compute-next for mthaddon mp241941
    UNIT OK: passed

UNIT Results (max last 5 lines):
  nova_compute_hooks 132 13 90% 79, 97-98, 125, 191, 249, 254-255, 261, 265-268
  nova_compute_utils 228 110 52% 161-217, 225, 230-233, 268-270, 277, 281-284, 292-300, 304, 313-322, 335-354, 380-381, 385-386, 405-426, 443-453, 467-468, 473-474
  TOTAL 566 194 66%
  Ran 56 tests in 3.492s
  OK (SKIP=5)

Full unit test output: http://paste.ubuntu.com/9055859/
Build: http://10.98.191.181:8080/job/charm_unit_test/940/

UOSCI bot says:
charm_amulet_test #448 nova-compute-next for mthaddon mp241941
    AMULET OK: passed

AMULET Results (max last 5 lines):
  juju-test.conductor.15-basic-trusty-icehouse RESULT :
  juju-test.conductor DEBUG : Tearing down osci-sv07 juju environment
  juju-test.conductor DEBUG : Calling "juju destroy-environment -y osci-sv07"
  WARNING cannot delete security group "juju-osci-sv07-0". Used by another environment?
  juju-test INFO : Results: 3 passed, 0 failed, 0 errored

Full amulet test output: http://paste.ubuntu.com/9056022/
Build: http://10.98.191.181:8080/job/charm_amulet_test/448/

Thank you for the merge proposal. I've included a few minor suggestions in the inline comments.

LGTM