Bug: Bootstrap with spec file fails when no ssh-user is specified in the suite file.

[pdhiran]

Describe the bug
Cephadm bootstrap fails when no ssh-user is specified in suite file for spec file based cluster deployments.

works in this case :

  - test:
      name: Cephadm Bootstrap with apply-spec
      desc: Apply spec in Bootstrap with host location attributes
      module: test_bootstrap.py
      polarion-id: CEPH-83609796
      config:
        command: bootstrap
        base_cmd_args:
          verbose: true
        args:
          mon-ip: node1
          rhcs-version: 8.0
          release: rc
          ssh-user: cephuser
          apply-spec:
            - service_type: host
              address: true
              labels: apply-all-labels

Does not work when there is no ssh-user specified:

  - test:
      name: Cephadm Bootstrap with apply-spec
      desc: Apply spec in Bootstrap with host location attributes
      module: test_bootstrap.py
      polarion-id: CEPH-83609796
      config:
        command: bootstrap
        base_cmd_args:
          verbose: true
        args:
          mon-ip: node1
          rhcs-version: 8.0
          release: rc
          apply-spec:
            - service_type: host
              address: true
              labels: apply-all-labels

fail log : http://magna002.ceph.redhat.com/cephci-jenkins/cephci-run-2RC3C7/Cephadm_Bootstrap_with_apply-spec_0.log

To Reproduce
Do not provide a ssh-user for a spec based cluster deployment.

Expected behavior
cluster is deployed with default ssh user

Screenshots
error snippet :

Copying ssh key to host ceph-pdhiran-2rc3c7-node9 at address 10.0.65.104 failed!

 and code 234 on 10.0.58.131
Traceback (most recent call last):
  File "/home/pdhiran/cephci/run.py", line 839, in run
    rc = test_mod.run(
  File "/home/pdhiran/cephci/tests/cephadm/test_bootstrap.py", line 593, in run
    out, err = method(config)
  File "/home/pdhiran/cephci/ceph/ceph_admin/bootstrap.py", line 324, in bootstrap
    out, err = self.installer.exec_command(
  File "/home/pdhiran/cephci/ceph/ceph.py", line 2305, in exec_command
    return self.node.exec_command(cmd=cmd, **kw)
  File "/home/pdhiran/cephci/ceph/ceph.py", line 1700, in exec_command
    raise CommandFailed(
ceph.ceph.CommandFailed: cephadm --verbose --image registry-proxy.engineering.redhat.com/rh-osbs/rhceph:8-208 bootstrap --mon-ip 10.0.58.131 --apply-spec /tmp/tmpxifskucw.yaml returned 
Copying ssh key to host ceph-pdhiran-2rc3c7-node2 at address 10.0.59.92 failed!


Copying ssh key to host ceph-pdhiran-2rc3c7-node3 at address 10.0.57.179 failed!


Copying ssh key to host ceph-pdhiran-2rc3c7-node4 at address 10.0.214.126 failed!


Copying ssh key to host ceph-pdhiran-2rc3c7-node5 at address 10.0.214.21 failed!


Copying ssh key to host ceph-pdhiran-2rc3c7-node6 at address 10.0.212.123 failed!


Copying ssh key to host ceph-pdhiran-2rc3c7-node7 at address 10.0.66.76 failed!


Copying ssh key to host ceph-pdhiran-2rc3c7-node8 at address 10.0.65.141 failed!


Copying ssh key to host ceph-pdhiran-2rc3c7-node9 at address 10.0.65.104 failed!

 and code 234 on 10.0.58.131

Environment
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python version, operating system, command used etc.

Additional context
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