baseport for content cluster nodes doesn't work well for all node types

[kawatea]

Describe the bug
When we set baseport for content cluster nodes, it works for storagenode but doesn't work well for distributor/searchnode.
distributor-base-port also doesn't work at all.

To Reproduce
Steps to reproduce the behavior:

1. Deploy one content cluster with baseport

  <content id="test2" version="1.0">
    <redundancy>1</redundancy>
    <documents>
      <document type="test2" mode="index" />
    </documents>
    <nodes>
      <node hostalias="node1" distribution-key="0" baseport="20000"/>
    </nodes>
  </content>

2. Add another content cluster before the existing cluster

  <content id="test1" version="1.0">
    <redundancy>1</redundancy>
    <documents>
      <document type="test1" mode="index" />
    </documents>
    <nodes>
      <node hostalias="node1" distribution-key="0" baseport="10000"/>
    </nodes>
  </content>

  <content id="test2" version="1.0">
    <redundancy>1</redundancy>
    <documents>
      <document type="test2" mode="index" />
    </documents>
    <nodes>
      <node hostalias="node1" distribution-key="0" baseport="20000"/>
    </nodes>
  </content>

3. See warnings and restart messages

WARNING distributor cannot reserve port 10000 on vespa-container: Already reserved for storagenode. Using default port range from 19109
WARNING distributor cannot reserve port 10001 on vespa-container: Already reserved for storagenode. Using default port range from 19110
WARNING distributor cannot reserve port 10002 on vespa-container: Already reserved for storagenode. Using default port range from 19111
WARNING distributor2 cannot reserve port 20000 on vespa-container: Already reserved for storagenode2. Using default port range from 19120
WARNING distributor2 cannot reserve port 20001 on vespa-container: Already reserved for storagenode2. Using default port range from 19121
WARNING distributor2 cannot reserve port 20002 on vespa-container: Already reserved for storagenode2. Using default port range from 19122
WARNING Change(s) between active and new application that require restart:
In cluster 'test2' of type 'content':
    Restart services of type 'distributor' because:
        1) stor-communicationmanager.mbusport has changed from 19109 to 19120
stor-communicationmanager.rpcport has changed from 19110 to 19121
stor-status.httpport has changed from 19111 to 19122
In cluster 'test2' of type 'search':
    Restart services of type 'searchnode' because:
        1) # Port to use for the rpcserver.
proton.rpcport has changed from 19103 to 19114
# Port to use for the web server
proton.httpport has changed from 19107 to 19118
# Connect spec for transactionlog server.
# TODO Consider not using RPC at all
proton.tlsspec has changed from "tcp/vespa-container:19108" to "tcp/vespa-container:19119"
# Port number to use for listening.
translogserver.listenport has changed from 19108 to 19119

Expected behavior
baseport setting should work properly for distributor/searchnode and we should be able to avoid restarting services.

Environment (please complete the following information):

• OS: Ubuntu
• Infrastructure: self-hosted (observed the same behavior on Kubernetes)
• Versions 18.04

Vespa version
8.339.15

Additional context
We want to avoid restarting unrelated distributor/storagenode/searchnode when adding/removing/updating content clusters because it causes outage for a while.
baseport setting works for storagenode but doesn't work well for distributor (distributor-base-port also doesn't work) and doesn't affect searchnode.