common: configure_cache_path: Invalid conf generated

[NGenetzky]

1. by using -e for echo you are actually removing the '\n' which needs to be in the output.
2. This also adds an absolute path into the project - which is a problem for shared projects.
3. this also appends to the file again if called again - which might not be a problem, but it is a disadvantage.

→ bash -x echo_badly.sh 
+ CACHE_DIR=/a/b/c
+ DOWNLOAD_CACHE=dl
+ CONF_FILE=foo.conf
+ echo -e '\nPREMIRRORS_prepend = "git://.*/.* file:///a/b/c/dl \ \n' 'ftp://.*/.* file:///a/b/c/dl \ \n' 'http://.*/.* file:///a/b/c/dl \ \n' 'https://.*/.* file:///a/b/c/dl "\n'
+ cat foo.conf

PREMIRRORS_prepend = "git://.*/.* file:///a/b/c/dl \ 
 ftp://.*/.* file:///a/b/c/dl \ 
 http://.*/.* file:///a/b/c/dl \ 
 https://.*/.* file:///a/b/c/dl "

Similar comments here about adding absolute path into the project. These variables are easily configured many other more proper ways, consider using them.

  echo "DL_DIR = \"${CACHE_DIR}/${DOWNLOAD_CACHE}\"" >> ${CONF_FILE}
  echo "SSTATE_DIR = \"${CACHE_DIR}/${SSTATE_CACHE}\"" >> ${CONF_FILE}