Check tarantool dependence working under tt

When luarocks is running from under tt we need to
use another tarantool dependency check method because
luarocks are not running inside tarantool and has no
access to _TARANTOOL variable.

Part of the tarantool/tt#114

src/luarocks/util.lua

@@ -642,6 +642,16 @@ function util.get_rocks_provided(rockspec)
       rocks_provided["tarantool"] = tarantool_version.."-1"
    end
 
+   -- If luarocks is launched from tt, it cannot directly access
+   -- the _TARANTOOL variable.
+   local tarantool_ver_env = os.getenv("TT_CLI_TARANTOOL_VERSION")
+   if tarantool_ver_env ~= nil then
+      local tarantool_version = tarantool_ver_env:match("([^-]+)-")
+      if tarantool_version ~= nil then
+         rocks_provided["tarantool"] = tarantool_version.."-1"
+      end
+   end
+
    if cfg.rocks_provided then
       util.deep_merge_under(rocks_provided, cfg.rocks_provided)
    end