refactor: bash scripts [stip travis]

- shellchecke and shfmt checked and formatted
- indentation 2 spaces
- redirect errors to stderr
- short if where possible
- add function string to clarify visuaally identify its a funtion
- make [ ... ] to [[ ... ]]
- use == for comparision
- use cat based notes
- remove unecessary spaces
- double quotes where needed

build/common/worker/install_app.sh

@@ -6,11 +6,11 @@ APP_BRANCH=${3}
 
 cd /home/frappe/frappe-bench/
 
-. env/bin/activate
+env/bin/activate
 
 cd ./apps
 
-[ "${APP_BRANCH}" ] && BRANCH="-b ${APP_BRANCH}"
+[[ -n "${APP_BRANCH}" ]] && BRANCH="-b ${APP_BRANCH}"
 
 git clone --depth 1 -o upstream ${APP_REPO} ${BRANCH} ${APP_NAME}
-pip3 install --no-cache-dir -e /home/frappe/frappe-bench/apps/${APP_NAME}
+pip3 install --no-cache-dir -e /home/frappe/frappe-bench/apps/${APP_NAME}