Enable MbedTLS in the integration tests #2805

Job	Run time
build_and_test (rustcrypto)	10m 3s
build_and_test (openssl, alloc)	7m 6s
build_and_test (rustcrypto, alloc)	5m 48s
build_and_test (rustcrypto, os)	28m 58s
build_and_test (mbedtls, alloc)	7m 41s
build_and_test (mbedtls, os)	12m 35s
build_and_test (openssl, os)	10m 48s
build_and_test (mbedtls)	4m 42s
build_and_test (openssl)	6m 59s
	1h 34m 40s

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