glidein_config sometime is deleted or truncated
Testing #12705 I noticed 2 problems with glidein_config:
1. (not critical) if failing before reading the configuration file with the append function, the wrapper is appending lines to the glidein_config file instead of adding unique lines
2. (critical) sometime old entries disappear form the file: this means that the file is deleted or truncated before adding new entries. Before periodic scripts only one process at the time was accessing this file. Now periodic scripts could be concurrent. A possibility is that 2 updates are conflicting: while one starts writing the file a second one is getting the empty file and then is overwriting with the file resulting form this one.
This is not affecting other system scripts because by the time the periodic scripts start, all other scripts executed already. But is critical for the correct execution/communication of periodic scripts.