[Bash-Completion] Fix bash completon for files paths

Changes:
  * fix for command `rally task start --task [TAB]' - now
    it shows filepaths choices
  * introduces function _rally_filedir as replacement for
    _filedir - this fixes issue `._filedir: command not found'
    in case if /etc/bash_completion routines are not loaded
  * small refactoring in rally bash completion

Change-Id: Ib5e15a20c52ba3ccec32424d9404d2a929d82958
Closes-Bug: #1470006

etc/rally.bash_completion

@@ -1,6 +1,18 @@
-
 #!/bin/bash
 
+# Standalone _filedir() alternative.
+# This exempts from dependence of bash completion routines
+function _rally_filedir()
+{
+    test "${1}" \
+        && COMPREPLY=( \
+            $(compgen -f -- "${cur}" | grep -E "${1}") \
+            $(compgen -o plusdirs -- "${cur}") ) \
+        || COMPREPLY=( \
+            $(compgen -o plusdirs -f -- "${cur}") \
+            $(compgen -d -- "${cur}") )
+}
+
 _rally()
 {
     declare -A SUBCOMMANDS
@@ -44,7 +56,6 @@ _rally()
     OPTS["verify_start"]="--deployment --set --regex --tempest-config --no-use"
     OPTS["verify_use"]="--verification"
 
-
     for OPT in ${!OPTS[*]} ; do
         CMD=${OPT%%_*}
         CMDSUB=${OPT#*_}
@@ -57,22 +68,19 @@ _rally()
     local cur="${COMP_WORDS[COMP_CWORD]}"
     local prev="${COMP_WORDS[COMP_CWORD-1]}"
 
-    if [[ $cur =~ (\.|\~|\/).* ]] ; then
-        _filedir
+    if [[ $cur =~ ^(\.|\~|\/) ]] || [[ $prev =~ ^--out(|put-file)$ ]] ; then
+        _rally_filedir
+    elif [[ $prev =~ ^--(task|filename)$ ]] ; then
+        _rally_filedir "\.json|\.yaml|\.yml"
     elif [ $COMP_CWORD == "1" ] ; then
         COMPREPLY=($(compgen -W "$COMMANDS" -- ${cur}))
     elif [ $COMP_CWORD == "2" ] ; then
         COMPREPLY=($(compgen -W "${SUBCOMMANDS[${prev}]}" -- ${cur}))
-    else
-        if [ $prev == "--filename" ] ; then
-            _filedir "@(json|ya?ml)"
-        elif [ $prev == "--output-file" ] || [ $prev == "--out" ]; then
-            _filedir
     else
         COMMAND="${COMP_WORDS[1]}_${COMP_WORDS[2]}"
         COMPREPLY=($(compgen -W "${OPTS[$COMMAND]}" -- ${cur}))
     fi
-    fi
     return 0
 }
-complete -F _rally rally
+
+complete -o filenames -F _rally rally