Remove the redundant `execute` command for proc execution

[olttwa]

As an admin,
I don't want users to type execute everytime they want to execute a proc.

Current scenario:

proctor execute create-some-infra-one ARG_ONE=a ARG_TWO=b
proctor execute create-some-infra-two ARG_THREE=c ARG_FOUR=d

Better scenario:

proctor create-some-infra-one ARG_ONE=a ARG_TWO=b
proctor create-some-infra-two ARG_THREE=c ARG_FOUR=d

This will also help move towards resolving #32