Make logs functions consistent with stdlib's logging module

[jonathanmetzman]

Superseeds: https://github.com/google/clusterfuzz/pull/3793. Examples:

1. Most logging libraries don't make you write "log_" before each function, but in CF we do. (e.g. "logs.log_error" instead of "logs.error".
2. Most logging libraries call it "warning" not "warn". CF does "warn".
3. Most logging libraries have an "info" function. In CF, this is called "log".