Fix unescape of backslash of variable's value in nuxeo.conf

When defining a variable whose value contains a double-backslash in nuxeo.conf, the variable gets redefined in the END block with a value containing only a single backslash.

How to reproduce:

• unzip a 2021 Nuxeo distribution and install hot fix 2021-HF02
• add the following variable at the beginning of file nuxeo.conf:

  nuxeo.var1=\\nuxeo
  

• execute command nuxeoctl configure

Expected result: the following block is added to the nuxeo.conf file:

### BEGIN - DO NOT EDIT BETWEEN BEGIN AND END ###
server.status.key=********
### END - DO NOT EDIT BETWEEN BEGIN AND END ###

Actual result: the following block is added to the nuxeo.conf file, see the redefinition of variable nuxeo.var with a different value:

### BEGIN - DO NOT EDIT BETWEEN BEGIN AND END ###
nuxeo.var1=\nuxeo
server.status.key==********
### END - DO NOT EDIT BETWEEN BEGIN AND END ###

This issue started with hot fix 2021-HF02.