Add support for SLAPOS_CONFIGURATION and SLAPOS_CLIENT_CONFIGURATION envvars.

Also update doc

documentation/slapos.usage.rst

@@ -6,10 +6,10 @@ SlapOS command line usage
 Note:
 -----
  * Default configuration file of "Node" commands if not explicitly defined (slapos node, slapos supervisor) is:
-    /etc/opt/slapos/slapos.cfg
+    /etc/opt/slapos/slapos.cfg or value of SLAPOS_CONFIGURATION environment variable if exists.
 
  * Default configuration file of "Client" commands if not explicitly defined (slapos request, slapos supply, ...) is:
-    ~/.slapos/slapos.cfg
+    ~/.slapos/slapos.cfg or value of SLAPOS_CLIENT_CONFIGURATION environment variable if exists.
 
  * Default log file for Node commands is /var/log/[slapos-node-software.log | slapos-node-instance.log | slapos-node-report.log]. This one requires working log in slapgrid, currently log/console is a total mess.
 

slapos/entry.py

@@ -41,8 +41,12 @@ from slapos.grid.svcbackend import supervisord
 from slapos.grid.svcbackend import supervisorctl
 from slapos.register.register import main as register
 
-GLOBAL_SLAPOS_CONFIGURATION = '/etc/opt/slapos/slapos.cfg'
-USER_SLAPOS_CONFIGURATION = '~/.slapos/slapos.cfg'
+GLOBAL_SLAPOS_CONFIGURATION = os.environ.get(
+    'SLAPOS_CONFIGURATION',
+    '/etc/opt/slapos/slapos.cfg')
+USER_SLAPOS_CONFIGURATION = os.environ.get(
+    'SLAPOS_CLIENT_CONFIGURATION',
+    os.environ.get('SLAPOS_CONFIGURATION', '~/.slapos/slapos.cfg'))
 
 class EntryPointNotImplementedError(NotImplementedError):
   def __init__(self, *args, **kw_args):