change regex search string for linux distros

[gojun077]

To detect the Linux distribution type, setup.py checks /etc/*-release files which matches two files on Amazon Linux (new and old versions):

- /etc/os-release
- /etc/system-release

On Amazon Linux 2, "system-release" contains the single line

• Amazon Linux 2 While on Amazon Linux < v2 "system-release" returns
• Amazon Linux AMI release 2018.03

On Amazon Linux 2, "os-release" looks like the following:

NAME="Amazon Linux"
VERSION="2"
ID="amzn"
ID_LIKE="centos rhel fedora"
VERSION_ID="2"
PRETTY_NAME="Amazon Linux 2"
ANSI_COLOR="0;33"
CPE_NAME="cpe:2.3:o:amazon:amazon_linux:2"
HOME_URL="https://amazonlinux.com/"
``
On Amazon Linux < v2, "os-release" looks like:

NAME="Amazon Linux AMI" VERSION="2018.03" ID="amzn" ID_LIKE="rhel fedora" VERSION_ID="2018.03" PRETTY_NAME="Amazon Linux AMI 2018.03" ANSI_COLOR="0;33" CPE_NAME="cpe:/o:amazon:linux:2018.03:ga" HOME_URL="http://aws.amazon.com/amazon-linux-ami/"

In `setup.py` the regex current matches the string
    - "Amazon Linux AMI"
But it this is shortened to just
    - "Amazon Linux"

both old and new versions of Amazon Linux will be matched by
the regex allowing the collectd-cloudwatch plugin to be
installed.

[gojun077]

Oops! I didn't see that someone else has opened a pull request for the same change! Please disregard this request...