I've been there too and searched everywhere how /usr/libexec/java_home works but I couldn't find any information on how it determines the available Java Virtual Machines it lists.
I've experimented a bit and I think it simply executes a ls /Library/Java/JavaVirtualMachines and then inspects the ./<version>/Contents/Info.plist of all runtimes it finds there.
It then sorts them descending by the key JVMVersion contained in the Info.plist and by default it uses the first entry as its default JVM.
I think the only thing we might do is to change the plist: sudo vi /Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Info.plist and then modify the JVMVersion from 1.8.0 to something else that makes it sort it to the bottom instead of the top, like !1.8.0.
Something like:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
...
<dict>
...
<key>JVMVersion</key>
<string>!1.8.0</string> <!-- changed from '1.8.0' to '!1.8.0' -->`
and then it magically disappears from the top of the list:
/usr/libexec/java_home -verbose
Matching Java Virtual Machines (3):
1.7.0_45, x86_64: "Java SE 7" /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/Home
1.7.0_09, x86_64: "Java SE 7" /Library/Java/JavaVirtualMachines/jdk1.7.0_09.jdk/Contents/Home
!1.8.0, x86_64: "Java SE 8" /Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home
Now you will need to logout/login and then:
java -version
java version "1.7.0_45"
:-)
Of course I have no idea if something else breaks now or if the 1.8.0-ea version of java still works correctly.
You probably should not do any of this but instead simply deinstall 1.8.0.
However so far this has worked for me.