[master] Do not break repo files with multiple line values on "yumpkg"

[meaksh]

This PR ports #53293 to master branch, and fixes an issue at 2019.2.x release.

---

What does this PR do?

This PR fixes an issue happening when running either pkg.mod_repo and pkg.del_repo from the yumpkg module when a repo file has multiline values.

Given this repo file as example in /etc/yum.repos.d/salt-products-testing.repo:

[systemsmanagement_saltstack_products_testing]
name=Salt releases for SLE-based SUSE products testing (RHEL_7)
failovermethod=priority
gpgkey=http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/repodata/repomd.xml.key
enabled=1
baseurl=http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
 http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
gpgcheck=1
type=rpm-md

Previous Behavior

$ salt-call --local pkg.mod_repo systemsmanagement_saltstack_products_testing
local:
    ----------
    /etc/yum.repos.d/salt-products-testing.repo:
        ----------
        systemsmanagement_saltstack_products_testing:
            ----------
            baseurl:
                http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
                http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
            enabled:
                1
            failovermethod:
                priority
            gpgcheck:
                1
            gpgkey:
                http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/repodata/repomd.xml.key
            name:
                Salt releases for SLE-based SUSE products testing (RHEL_7)
            type:
                rpm-md

After that, the file is already broken. Notice there is no multiline value anymore and instead there is a buggy http attribute:

$ cat /etc/yum.repos.d/salt-products-testing.repo
[systemsmanagement_saltstack_products_testing]
http=//download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
name=Salt releases for SLE-based SUSE products testing (RHEL_7)
failovermethod=priority
gpgkey=http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/repodata/repomd.xml.key
enabled=1
baseurl=http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
gpgcheck=1
type=rpm-md

New Behavior

The repo file preserves the multiline values:

$ cat /etc/yum.repos.d/salt-products-testing.repo
[systemsmanagement_saltstack_products_testing]
name=Salt releases for SLE-based SUSE products testing (RHEL_7)
failovermethod=priority
gpgkey=http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/repodata/repomd.xml.key
enabled=1
baseurl=http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
 http://download.opensuse.org/repositories/systemsmanagement:/saltstack:/products:/testing/RHEL_7/
gpgcheck=1
type=rpm-md

Tests written?

Yes

Commits signed with GPG?

Yes