[tarantoolctl] add an ability to specify an app folder

[opomuc]

Consider following scenario

--/
--/project/
--/project/app_1
--/project/app_1/init.lua
--/project/app_1/.tarantoolctl
--/...
--/project/app_2
--/project/app_2/init.lua
--/project/app_2/.tarantoolctl
--/...
--/project/run
--/project/data
--/project/logs

.tarantoolctl:
default_cfg = {
    pid_file  = "../project/run",
    wal_dir   = "../project/data",
    memtx_dir = "../project/data",
    vinyl_dir = "../project/data",
    username  = "vagrant",
}
instance_dir = "../project/"

# cd project/app_1
# tarantoolctl start app_1

I want tarantoolctl to look for init.lua file in the following directory and create all necessary files under correct folder structure