bootloader: Strip prior console settings

Prior to this change, source images could introduce variation in the
the result of the bootloader element results, if the configuration
is changed later which would could re-introduce arguments not desired
which come from the source image.

Since we assert, bsaed upon user supplied input, new console configuration
we now strip the console configuration from /etc/default/grub configuration
before starting to work on putting in place the user's desired end state.

This also ends up helping reduce/remove the possibility of multiple
console elements as some were sourcing from the original source image.

Change-Id: Ia1f9987d989f1d0e1cbda619f7abdf7005b47fbc

diskimage_builder/elements/bootloader/finalise.d/50-bootloader

@@ -87,6 +87,16 @@ if [[ -L $GRUBENV ]]; then
     rm -f $GRUBENV
 fi
 
+# NOTE(TheJulia): Explicitly strip out embedded console settings
+# in the source's grub defaults. This prevents re-introduction later.
+# Intentionally matching 'console=ttyS0,115200n8 console=tty0'
+# Also globally matches so it can handle 'console=tty0 stuff console=tty1'
+# ... and also matches
+# 'console=ttyS0,112500n81 console=ttyS1,n8 console=tty0'
+if [[ -f /etc/default/grub ]]; then
+    sed -i 's/\<console=[[:alnum:],]*[[:space:]]*//g' /etc/default/grub
+fi
+
 echo "GRUB_DEVICE=LABEL=${DIB_ROOT_LABEL}" >> /etc/default/grub
 echo 'GRUB_DISABLE_LINUX_UUID=true' >> /etc/default/grub
 echo "GRUB_TIMEOUT=${DIB_GRUB_TIMEOUT:-5}" >>/etc/default/grub

releasenotes/notes/bootloader-strip-source-console-param-b73b603df0b01dc9.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    The ``bootloader`` element now strips prior explicit console settings
+    from the ``/etc/default/grub`` file, in order to prevent accidential
+    re-introduction of prior settings when grub configuration is manually
+    updated later.