Decrease performance tests duration in stability testing #233
Description
perf.test_insert ... (30.038s) Ok
perf.test_select ... (30.094s) Ok
There is no sense to spin for 30 seconds on them in stability testing. I would run them for a long duration only when a particular environment variable is set, say LUATEST_PERFTEST=1. In tarantool/luatest#186 we can set this variable from luatest itself, when perf. test mode is requested.