Add python-mock and python-coverage for osx.

See http://answers.ros.org/question/153156/rosdep-error-while-i-try-to-install-ros-on-os-x-108/
Merge pull request #3873 from NikolausDemmel/patch-1

Add python-mock and python-coverage for osx.
bump libg2o for hydro
add docs for capabilities in Indigo
Merge pull request #3874 from vrabaud/master

bump libg2o for hydro
Merge pull request #3875 from ros/capabilities_doc_indigo

add docs for capabilities in Indigo
nav2_platform: 0.0.1-0 in 'hydro/distribution.yaml' [bloom]
frontier_exploration: 0.2.1-0 in 'hydro/distribution.yaml' [bloom]
Merge pull request #3877 from paulbovbel/bloom-frontier_exploration-7

frontier_exploration: 0.2.1-0 in 'hydro/distribution.yaml' [bloom]
Merge pull request #3876 from paulbovbel/bloom-nav2_platform-0

nav2_platform: 0.0.1-0 in 'hydro/distribution.yaml' [bloom]
common_tutorials: 0.1.7-0 in 'indigo/distribution.yaml' [bloom]
Merge pull request #3880 from stonier/bloom-common_tutorials-1

common_tutorials: 0.1.7-0 in 'indigo/distribution.yaml' [bloom]
bwi_common: add doc and source repository to Hydro
Merge pull request #3881 from jack-oquin/master

bwi_common: add doc and source repository to Hydro
capabilities: 0.1.0-0 in 'indigo/distribution.yaml' [bloom]
capabilities: 0.1.0-0 in 'hydro/distribution.yaml' [bloom]
capabilities: 0.1.0-0 in 'groovy/distribution.yaml' [bloom]
Merge pull request #3882 from wjwwood/bloom-capabilities-0

capabilities: 0.1.0-0 in 'indigo/distribution.yaml' [bloom]
Merge pull request #3883 from wjwwood/bloom-capabilities-1

capabilities: 0.1.0-0 in 'hydro/distribution.yaml' [bloom]
Merge pull request #3884 from wjwwood/bloom-capabilities-2

capabilities: 0.1.0-0 in 'groovy/distribution.yaml' [bloom]