华为云yum install报错404 repodata/repomd.xml Not Found

# 问题现象

```
[root@ecs-78121 yum.repos.d]# yum install -y xxx
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirrors.aliyun.com

base                                                                              | 3.6 kB  00:00:00     
https://repo.huaweicloud.com/epel/7/x86_64/repodata/repomd.xml: [Errno 14] HTTPS Error 404 - Not Found
Trying other mirror.
To address this issue please refer to the below wiki article

https://wiki.centos.org/yum-errors

If above article doesn't help to resolve this issue please use https://bugs.centos.org/.

One of the configured repositories failed (Extra Packages for Enterprise Linux 7 - x86_64),
 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. Run the command with the repository temporarily disabled
            yum --disablerepo=epel ...

4. Disable the repository permanently, 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 epel
        or
            subscription-manager repos --disable=epel

5. 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=epel.skip_if_unavailable=true

failure: repodata/repomd.xml from epel: [Errno 256] No more mirrors to try.
https://repo.huaweicloud.com/epel/7/x86_64/repodata/repomd.xml: [Errno 14] HTTPS Error 404 - Not Found

```

# 解决办法
步骤1：
```
cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
```

步骤2：
```
cd  /etc/yum.repos.d/
vim epel.repo
```

把里面所有的
`repo.huaweicloud.com` 替换为
`mirrors.aliyun.com`