vlib: print logs to stderr if interactive or nosyslog set

vlib: print logs to stderr if interactive or nosyslog set

If VPP is started in interactive mode, instead of sending logs to syslog
server we print them directly to stderr.
Output is colorized, but that can be turned off with unix { nocolor }

Type: improvement
Change-Id: I9a0f0803e4cba2849a6efa0b6a86b9614ed33ced
Signed-off-by: Damjan Marion <damarion@cisco.com>