Improve error messages for API calls

Example before: {"errorMessage":"Undefined offset: 0 [8]"}
Example after: {"errorMessage":"Error at \/usr\/local\/etc\/inc\/util.inc:952 - Undefined offset: 0 (errno=8)"}

While there, turn the probing upside down for general sanity:

o Only pull dmesg output once
o Pattern-match one pattern only
o Anchor the match to the line start

(get_interface_list) Properly handle an interface not appearing in dmesg

Also see: http://www.openssh.com/txt/release-7.0

The console would refuse to assign an IP that was used by the
PPTP or L2TP server (surprisingly not PPPoE).  This rule changed
during the MPD4 -> MDP5 migration, so remove that code.  Also,
the subnet check was never executed, good time to remove it as
well.

Spotted by: @fabianfrz

Reported by: @Antonio-Prado

(mvc) more work on migrations, fix autoloader, serialize to config when all steps for this model are finished

(mvc) BaseModel add getVersion() to retrieve the running config version, commit changes to in memory config after every migration step.

Errors will be send to syslog, current policy is to always upgrade and ignore migration errors.
(there's not really a way back, other then undo pkg install and revert the full config)

(Base) Default to inf rows not 9999

(base) Do not encourage overriding getModel()

Overriding getModel() is not to be done lightly. The code relies on the same object being there through multiple calls to getModel(). Any overriding methods should preserve this same behavior. For this reason, we should not encourage tinkering with this in a comment, better be silent on the matter.

ApiMutableTableModelControllerBase