don't overwrite existing server config
don't overwrite existing server config

This is required e.g. for OCA/server-tools: travis config generates a
server configuration file, which is required by the server_environment
module. f4d9198 would overwrite that file causing build failures.

ERP-Ukraine/maintainer-quality-tools,acsone/maintainer-quality-tools,acsone/maintainer-quality-tools,ERP-Ukraine/maintainer-quality-tools,ilyasProgrammer/maintainer-quality-tools,Endika/maintainer-quality-tools,ilyasProgrammer/maintainer-quality-tools,OCA/maintainer-quality-tools,gurneyalex/maintainer-quality-tools,dreispt/maintainer-quality-tools,Endika/maintainer-quality-tools,gurneyalex/maintainer-quality-tools,OCA/maintainer-quality-tools,acsone/maintainer-quality-tools,gurneyalex/maintainer-quality-tools,dreispt/maintainer-quality-tools,dreispt/maintainer-quality-tools,OCA/maintainer-quality-tools,ERP-Ukraine/maintainer-quality-tools