makebuildserver: do not provision excessive NDKs

When a new minor version of an NDK is released, it replaces an older one,
e.g. r16 with r16b (see commit 6f295cb). But old NDK package remains in
the cache and provisioning script unpacks it too as it matches the mask.

Fix NDK provisioning to unzip only while-listed versions.

buildserver/provision-android-ndk

@@ -14,8 +14,7 @@ if [ ! -e $NDK_BASE/r10e ]; then
     mv android-ndk-r10e r10e
 fi
 
-for f in /vagrant/cache/android-ndk-r[1-9][0-9]*-linux-x86_64.zip; do
-    version=`echo $f |sed  's,.*\(r[1-9][0-9][a-z]\?\).*,\1,'`
+for version in r11c r12b r13b r14b r15c r16b; do
     if [ ! -e ${NDK_BASE}/${version} ]; then
         unzip /vagrant/cache/android-ndk-${version}-linux-x86_64.zip > /dev/null
         mv android-ndk-${version} ${version}