Fix node_exclusive handling in process dispatcher

Test and fix for OOIION-816
Release Version 2.0.19
Bump Version to 2.0.20-dev
Merge pull request #918 from labisso/OOIION-816

Fix node_exclusive handling in process dispatcher
Add route to SGS to delete attachments
Return value from RR delete attachment
Bump ion to include workflow timeout
Bump ion again
Release Version 2.0.20
Bump Version to 2.0.21-dev
update device extended resources to reflect current aggregate and rollup status design
Merge branch 'master' of github.com:ooici/coi-services
Now properly handling the agent parameters aparam_rollup_status and aparam_child_agg_status for propagation of updates triggered by a DeviceAggregateStatusEvent from a child. New test test_platform_status_small_network_5 to verify the propagation with a multi-level 5-platform network.
merge upstream/master
adjust comment
add test_platform_status_small_network_5_1: Test of status propagation in a small network of 5 platforms with multiple levels, and 1 instrument,
with all updates triggered from the instrument.
Merge pull request #919 from daf/sgs_delete_attachment

Add route to SGS to delete attachments
Modify SGS attachment routes to use gateway_json_response
Merge pull request #921 from daf/sgs_attachment_returns

Modify SGS attachment routes to use gateway_json_response
Merge pull request #922 from lukecampbell/udunits

Adds UDUNITS to coi-services