Add warning to nodepool configs about changing cloud name

The cloud name is used to lookup cloud credentials in clouds.yaml, but
it is also used to determine names for things like mirrors within jobs.
As a result changing this value can impact running jobs as you need to
update DNS for mirrors (and possibly launch new mirrors) first. Add a
warning to help avoid problems like this in the future.

Change-Id: I9854ad47553370e6cc9ede843be3303dfa1f9f34

nodepool/nl01.opendev.org.yaml

@@ -46,6 +46,8 @@ labels:
 providers:
   - name: rax-dfw
     region-name: 'DFW'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: rax
     boot-timeout: 120
     launch-timeout: 600
@@ -148,6 +150,8 @@ providers:
             key-name: infra-root-keys-2020-05-13
   - name: rax-iad
     region-name: 'IAD'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: rax
     boot-timeout: 120
     launch-timeout: 600
@@ -160,6 +164,8 @@ providers:
 
   - name: rax-ord
     region-name: 'ORD'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: rax
     boot-timeout: 120
     # Under load, this region can take a very long time to launch instances,

nodepool/nl02.opendev.org.yaml

@@ -64,6 +64,8 @@ labels:
 providers:
   - name: inmotion-iad3
     region-name: 'iad3'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: inmotion
     boot-timeout: 120
     launch-timeout: 300

nodepool/nl03.opendev.org.yaml

@@ -102,6 +102,8 @@ labels:
 providers:
   - name: vexxhost-ca-ymq-1
     region-name: 'ca-ymq-1'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: vexxhost
     boot-timeout: 120
     rate: 0.001
@@ -210,6 +212,8 @@ providers:
 
   - name: vexxhost-sjc1
     region-name: sjc1
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: vexxhost
     boot-timeout: 120
     rate: 0.001
@@ -361,6 +365,8 @@ providers:
 
   - name: linaro-regionone
     region-name: 'RegionOne'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: linaro
     boot-timeout: 600
     launch-timeout: 800
@@ -446,6 +452,8 @@ providers:
 
   - name: osuosl-regionone
     region-name: 'RegionOne'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: osuosl
     boot-timeout: 600
     launch-timeout: 800

nodepool/nl04.opendev.org.yaml

@@ -50,6 +50,8 @@ labels:
 providers:
   - name: ovh-bhs1
     region-name: 'BHS1'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: ovh
     boot-timeout: 120
     launch-timeout: 600
@@ -198,6 +200,8 @@ providers:
 
   - name: ovh-gra1
     region-name: 'GRA1'
+    # Changing this cloud value impacts things like mirror names in jobs.
+    # It should be changed carefully.
     cloud: ovh
     boot-timeout: 120
     launch-timeout: 600