CLI Commands use os.Exit/log.Fatalf instead of cobra's RunE, Args, and PreRun

[mynk8]

Reason/Context

There are several subtle input validation bugs in the arguments and the code is not fully utilizing the idiomatic features of cobra for handling errors and lifecycle.

Description

Here's a small list I can think of

• No Args validators -- manual len(args) checks with cmd.HelpFunc() + os.Exit(1) instead of cobra's ExactArgs, MinimumNArgs
• No PreRunE -- flag validation happens inside Run after network calls have started, instead of before
• SilenceErrors not set -- cobra prints errors on top of the command's own error output

Some example validation loopholes

• microcks login --sso-port 0 / --sso-port 65536 — passes invalid ports to HTTP listener
• microcks test --waitFor 5abc — crashes with os.Exit(1) (this was addressed in PR fix: exit with clear error when --waitFor value is not a valid number #271 as well)

Implementation ideas

No response