ocivm.sh: Allow projects to specify build VM name

Projects can now set a `buildvm` variable in their `config` file to
specify a unique name for their build VMs.  This allows multiple
projects to have running VMs simultaneously.

If a project does not provide a name, the build VM will be called
`aimeebuild`.

ocivm.sh

@@ -4,7 +4,6 @@ set -e
 
 . "${CONFIGDIR:=${PWD}}"/config
 
-name=build_yellow
 if ! ocivm list | grep -q localhost/cross-${target}; then
     ocivm import localhost/cross-${target}
 fi
@@ -12,7 +11,7 @@ ocivm \
     --log-level DEBUG \
     run \
     -m 8G \
-    -n ${name} \
+    -n ${buildvm:-aimeebuild} \
     -w /tmp/src \
     -v "${PWD}":/tmp/src \
     -v portagecache:/var/cache:size=16G \