overlayfs: all overlays unit

Application can depend on several overlayfs mount points. Provide a
systemd unit application can depend on to make sure all overlays are
mounted before it is started to avoid any race conditions

(From OE-Core rev: b38e194db0c6825f28c56123cf88af94d3f52beb)

Signed-off-by: Bruno Knittel <Bruno.Knittel@bruker.com>
Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/overlayfs.py

@@ -15,6 +15,9 @@ def escapeSystemdUnitName(path):
 def strForBash(s):
     return s.replace('\\', '\\\\')
 
+def allOverlaysUnitName(d):
+    return d.getVar('PN') + '-overlays.service'
+
 def mountUnitName(unit):
     return escapeSystemdUnitName(unit) + '.mount'
 
@@ -39,5 +42,7 @@ def unitFileList(d):
             fileList.append(mountUnitName(path))
             fileList.append(helperUnitName(path))
 
+    fileList.append(allOverlaysUnitName(d))
+
     return fileList