During 2.1.0-rc1 builds on ubuntu 18.04, use oob cmake instead compiling it if it doesn't exist

[matthewdarwin]

Once this issue #9787 is committed, it looks like the ubuntu provided cmake should be fine to use.
Thus the dependency checker should check for it instead of compiling one if it doesn't exist. This would reduce compile time.

Here is the output from the current dependency checker, which doesn't check for cmake:

=====================================================================================
======================= Starting EOSIO Dependency Install ===========================
Architecture: Linux
OS name: Ubuntu
OS Version: 18.04
CPU cores: 4
Physical Memory: 65G
Disk space total: 3602G
Disk space available: 2941G
[Ensuring package dependencies]
 - git ok
 - make ok
 - bzip2 ok
 - automake ok
 - libbz2-dev ok
 - libssl-dev ok
 - doxygen ok
 - graphviz ok
 - libgmp3-dev ok
 - autotools-dev ok
 - python2.7 ok
 - python2.7-dev ok
 - python3 ok
 - python3-dev ok
 - autoconf ok
 - libtool ok
 - curl ok
 - zlib1g-dev ok
 - sudo ok
 - ruby ok
 - libusb-1.0-0-dev ok
 - libcurl4-gnutls-dev ok
 - pkg-config ok
 - patch ok
 - lsb-release ok
 - gnupg ok
 - No required package dependencies to install.
```

[sanaraufx]

Fixed in rc3.