Decrease image size.

Dockerfile optimization leading to final image size reduction.

Before:
```bash
REPOSITORY               TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
apollomq                 1.7                 015a5af9b5ff        43 seconds ago      867.6 MB
```

After:
```bash
REPOSITORY               TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
apollomq                 1.7                 1f3214e2a798        5 seconds ago       659.8 MB
```
Signed-off-by: Tiago Pires <tandrepires@gmail.com>