[BUG] Upgrade fails if new volume specifies uid without gid

[r0mant]

Describe the bug

If there's a volume specification in the manifest like this:

  nodeProfiles:
    requirements:  
      volumes:
        - name: data
          path: /opt/data
          targetPath: /var/lib/data
          createIfMissing: true
          uid: 2020

The upgrade fails on the bootstrap phase with the following error:

User Message: failed to execute phase "/bootstrap"
        failed to run {[chown 2020: /opt/data] setting ownership of /opt/data to 2020: false}:
                exit status 1]

To Reproduce

Expected behavior

Logs

Environment (please complete the following information):

• OS [e.g. Redhat 7.4]:
• Gravity [e.g. 5.5.4]: 5.5+
• Platform [e.g. Vmware, AWS]:

Additional context