Longview can't auto-create MariaDB creds on Debian 9

[displague]

https://github.com/linode/longview/blob/536c819a3c2742e7ab8d13bc6ef7db620a44f48a/debian/linode-longview.config#L174 should be adjusted to fetch the username associated with the "Upgrades" account. In Debian9 with MariaDB (which is a silent replacement for mysql-server) this account is now "root" rather than "debian-sys-maint".

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Seen during Longview Client install:

Unable to automatically configure MySQL plugin:

Longview has detected MySQL running on this server but was unable to automatically configure the connection. To allow Longview to access your MySQL instance please run the following queries:

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root@debian:~# cat /etc/mysql/debian.cnf
# Automatically generated for Debian scripts. DO NOT TOUCH!
[client]
host     = localhost
user     = root
password =
socket   = /var/run/mysqld/mysqld.sock
[mysql_upgrade]
host     = localhost
user     = root
password =
socket   = /var/run/mysqld/mysqld.sock
basedir  = /usr

[displague]

The socket file should also be parsed from the config rather than assuming the default, as reported in https://github.com/linode/longview/issues/17