roles: Add role to install New Relic system monitor and php agent
roles: Add tasks in setup_newrelic to install nginx and php-fpm
monitoring plugin

Also added the necessary modification needed (enabling status pages
for nginx and php-fpm) in nginx's config for the plugin to work
roles/install_sphinx: Use `sed` to set pid file location for sphinx

Instead of templating the whole init.d script, now just the two values:
location of log directory and pid file are set using `sed` in the sphinx's
init.d script
restore_version/files: Remove duplicate code
restore_version/files: Give meaningful names (content based) to variables
roles/restore: Remove a tautological condition for creating database
configure_sphinx/tasks: Use shell return value instead of stdout of shell commands
configure_sphinx: Change variable used for setting location of sphinx's pidfile
roles/backup: Enable md5 validation of downloaded backup
mount.sh: Check whether `sshfs` is present before attempting to mount/unmount
setup_database/files: Fix typos and use meaningful variable names in install_udpates.sh
roles: Use shell return values instead of stdout for checking directory presence
roles/setup_database: Factorize conditionals by creating separate files

Instead of writing conditions on each task, moved the tasks to separate
files and applied conditions on their imports
roles/common: Make cache valid time 1 hour
roles: Factorize conditionals by creating separate files (for external tools)

Instead of writing conditions on each task, moved the tasks to separate
files and applied conditions on their imports (applied on roles to setup all
the external tools except imagick)
host_vars: Make changes to vars files to fix few typos and default values
imouto: Add ssh_command parameter in sshfs to enable passwordless login using vagrant's private key