Adb and fastboot completion supports zsh users.

Builtin command "type" in zsh doesn't support -t option and this
is resolved by checking the shell type prior to sourcing them.
Instead of using "type -t" explicitly, check_type() knows the the
type of the current shell and behaves accordingly.

Bug: 110629292
Test: (zsh) source build/envsetup.sh && lunch aosp_arm
      (bash) source build/envsetup.sh && lunch aosp_arm

Change-Id: Ie39e130e9cc87135cfd522abedba11ad5ac25261