Linux post module to download and run a command
change from vcmd_exec to a method in the module
check if curl is on the path
Merge pull request #2 from jvazquez-r7/post_download_exec_work

check if curl is on the path
Merge branch 'post_linux_manage_download_exec' of https://github.com/jasbro/metasploit-framework into jasbro-post_linux_manage_download_exec