Exeption message of 'live migration' is not appropriate

Fix bug 1194367

When do live-migration with RESTAPI body as:
{
    "os-migrateLive": {
        "host": "0443e9a1254044d8b99f35eace132080",
        "block_migration": false
    }
}

Customer would get the following exception:
{
    "badRequest": {
        "message": "host and block_migration must be specified.",
        "code": 400
    }
}

Update the exception to the following which is more accurate:
host, block_migration and disk_over_commit must be specified.

Change-Id: I87fbc8e9d287cd73084ae5e36dd7d6c0bcaec41c
Sane rest API rate limit defaults

The previous rate limit defaults were unusable in any deployment.
Rate limiting to 10 POSTS per minute and 50 servers per day seems
to low, especially when we can use quotas to actually limit the amount
of resources a user can consume.

Update docstring to explain what the rate limiting is used for.

Fixes bug 1178529

DocImpact changed default values

Change-Id: I8cc93423f76d9b0a5135adf69babc4ff355a0951
Merge "Exeption message of 'live migration' is not appropriate"
Merge "Sane rest API rate limit defaults"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp