amqp_client_SUITE: Use a dedicated AMQP-0-9-1 connection per testcase

... instead of a global one. Otherwise, one connection failure, even if
expected by a testcase, will affect all subsequent testcases negatively.

(cherry picked from commit ce5ba6d)

# Conflicts:
#	deps/rabbit/test/amqp_client_SUITE.erl

Author: dumbbell