fixing bug related to the new security features in Git. Some requests to versions were made as root

classes/elphel-misc-functions.bbclass

@@ -23,12 +23,29 @@ def version_update(path,file,evr):
     return res
     
 def revision_update(path,file):
-    import subprocess
+    import subprocess, os# , pwd for some reasons  pwd.getpwall() show some 3-user default, so read and parse etc/passwd
+    pef = None # , preexec_fn=pefuid
+    if (os.getuid() == 0):
+        uname = os.getlogin()
+        with open("/etc/passwd") as f:
+            for line in f:
+                line = line.strip()
+                a = line.split(':')
+                if a[0] == uname:
+                    pef = preexec_fn=demote(int(a[3]),int(a[2]));    
+                    break
     cmd = "cd "+path+"; git rev-list --count $(git log -1 --pretty=format:\"%H\" "+file+")..HEAD"
     try:
-        res = subprocess.check_output(cmd,stderr=subprocess.STDOUT,shell=True)
+        res = subprocess.check_output(cmd,stderr=subprocess.STDOUT,shell=True, preexec_fn=pef)
     except subprocess.CalledProcessError as e:
         res = "error_"+e.returncode
     res = str(int(res))
     res = res.strip(' \t\n\r')
     return res
+
+def demote(user_uid, user_gid):
+    import os
+    def result():
+        os.setgid(user_gid)
+        os.setuid(user_uid)
+    return result