suricatasc: Snug the processing of different commands

suricatasc: Snug the processing of different commands

Since all of the commands were following the same procedure, namely,
split the input extract the arguments, throw the error if required
argument is missing else send the command over to suricata, put all of
this in one compact function alongwith a dictionary for specifications
for different commands, the name of the argument, the type and if it is
required or not.
Following fixups come with this commit:
- Code becomes really cozy
- Split errors on a few commands are well handled
- No redundant code
- More readability

References redmine ticket #2793