Allow user to opt-out of the execd installation on the scheduler node.

Skip this on master
sge_install -x

Start by locating the sge_install entry point and tracing how installation behaves on the scheduler node. Confirm the meaning of the -x option and identify the existing installation test or validation path. Done means the scheduler node can opt out of execd installation while other installation behavior remains unchanged.

索引モデルが issue の本文から書いたものです。