Create parent directory for env file

[farshidtz]

Fixes #62

[MonicaisHer]

I tested device-onvif-camera with this PR's hook and disabled install hook.

I dont get .env.tmp: no such file or directory error from configure hook anymore, but there is no .env file has been created after I set a snap option:

$ sudo snap install edgex-device-onvif-camera_0.0.1-dev.20_amd64.snap --dangerous
edgex-device-onvif-camera 0.0.1-dev.20 installed
$ sudo snap set edgex-device-onvif-camera configs.writable-loglevel=DEBUG
$ sudo snap start edgex-device-onvif-camera.device-onvif-camera 
Started.

/var/snap/edgex-device-onvif-camera$ tree
.
├── common
├── current -> x1
└── x1

3 directories, 0 files

[farshidtz]

configs.writable-loglevel=DEBUG -> config.writable-loglevel=DEBUG?

[MonicaisHer]

configs.writable-loglevel=DEBUG -> config.writable-loglevel=DEBUG?

It works!

/var/snap/edgex-device-onvif-camera
├── common
├── current -> x1
└── x1
    └── config
        └── device-onvif-camera
            └── res
                └── device-onvif-camera.env
$ cat device-onvif-camera.env 
WRITABLE_LOGLEVEL="DEBUG"

[MonicaisHer]

@farshidtz Thanks for the changes!