Enable MbedTLS in the integration tests #2807

Job	Run time
build_and_test (rustcrypto, os)	27m 59s
build_and_test (mbedtls, alloc)	7m 51s
build_and_test (openssl)	7m 21s
build_and_test (mbedtls)	6m 24s
build_and_test (rustcrypto, alloc)	7m 14s
build_and_test (openssl, os)	9m 50s
build_and_test (openssl, alloc)	7m 47s
build_and_test (mbedtls, os)	11m 8s
build_and_test (rustcrypto)	7m 59s
	1h 33m 33s

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