I have installed Centos 7 in virtual box. The laptop used proxy to connect to internet. After installing Centos, I have added the "http_proxy","https_proxy" and "no_proxy" environment variables. Every thing works fine, I can access internet through browser, and all commands through command line like "yum", "wget" are also working. But when I install packstack and run "Packstack --allinone" command, I ended up with the following error,

Pre installing Puppet and discovering hosts' details[ ERROR ]

ERROR : Failed to run remote script, stdout: Loaded plugins: fastestmirror, langpacks
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was 
14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error"

stderr: Warning: Permanently added '10.0.2.15' (ECDSA) to the list of known hosts.
+ trap t ERR
+ yum install -y puppet hiera openssh-clients tar nc rubygem-json


One of the configured repositories failed (Unknown),
and yum doesn't have enough cached data to continue. At this point the only
safe thing yum can do is fail. There are a few ways to work "fix" this:

 1. Contact the upstream for the repository and get them to fix the problem.

 2. Reconfigure the baseurl/etc. for the repository, to point to a working
    upstream. This is most often useful if you are using a newer
    distribution release than is supported by the repository (and the
    packages for the previous distribution release still work).

 3. Disable the repository, so yum won't use it by default. Yum will then
    just ignore the repository until you permanently enable it again or use
    --enablerepo for temporary usage:

        yum-config-manager --disable <repoid>

 4. Configure the failing repository to be skipped, if it is unavailable.
    Note that yum will try to contact the repo. when it runs most commands,
    so will have to try and fail each time (and thus. yum will be be much
    slower). If it is a very temporary problem though, this is often a nice
    compromise:

        yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Cannot find a valid baseurl for repo: base/7/x86_64
++ t
++ exit 1

Please check log file /var/tmp/packstack/20151205-041435-Lew9UH/openstack-setup.log for more information
Additional information:
* A new answerfile was created in: /root/packstack-answers-20151205-041437.txt
* Time synchronization installation was skipped. Please note that unsynchronized time on server instances might   be   problem for some OpenStack components.

I have tried putting proxy variable in yum.conf file, if I do that I can't even run yum command. Please help me with this. Thank you.