Modify the ProcessMonitor class to have one less config parameter

It's a follow up patch, as agreed on the ProcessMonitor review
patch to coalesce the check_child_processes parameter into
check_child_process_interval.

When this parameter is set to 0, the feature is disabled.

Change-Id: I2d4d8c6a6b7c17d42d8455c98968f75bcefbb689
Closes-Bug: 1371705
Updated from global requirements

Change-Id: I0e72933320ac6f49b55ef9782c6c19fb7e997bcb
Disable PUT for IPv6 subnet attributes

In Juno we are not ready for allowing the IPv6 attributes on a subnet
to be updated after the subnet is created, because:
- The implementation for supporting updates is incomplete.
- Perceived lack of usefulness, no good use cases known yet.
- Allowing updates causes more complexity in the code.
- Have not tested that radvd, dhcp, etc. behave OK after update.

Therefore, for now, we set 'allow_put' to False for the two IPv6
attributes, ipv6_ra_mode and ipv6_address_mode. This prevents the
modes from being updated via the PUT:subnets API.

Closes-bug: #1378952

Change-Id: Id6ce894d223c91421b62f82d266cfc15fa63ed0e
update ml2_migration to reflect optional methods

This change conditionally executes the schema methods for versions that
support them.

Change-Id: I8a51ac04e62dfcfe1e0a2e69a17664d154f0d1d7
Closes-Bug: #1378732
Merge "Updated from global requirements"
Merge "Modify the ProcessMonitor class to have one less config parameter"
Merge "update ml2_migration to reflect optional methods"
Merge branch 'master' of https://github.com/openstack/quantum